Synchronous communication system



Jan. 4, 1938; H H s 2,104,570

SYNCHRONOUS COMMUNICATION SYSTEM Filed May 22, 1933 8 Sheets-Sheet lmvEN'roR HARRY J. NICHOL BYW.

ATTORN EY Jan. 4, 1938 H. J. NICHOLS SYNCHRONOUS COMMUNICATION SYSTEMFiled May 22, 1953 8 Sheets-Sheet 2 f ly, 1-5

HNVENTUR HA RY J,NICHOLS.

ATTORNEY Jan. 4, 1938. 2,104,570

H. J. NICHOLS SYNCHRONOUS COMMUNICATION SYSTEM Filed May 22, 1933 8Sheets-Sheet 5 PR/NTER- INVENTOR HARRY J. NICHOLS.

Fly. 2

ATTORN EY Jan. 4, v H, J ICH S SYNCHRONOUS COMMUNICATION SYSTEM FiledMay 22, 19:53 8 Sheets -Sheet 4 5. INVENTOR RY J. NICHOLS. 3217/ATTORNEY H. J. NlCHOLS Jan. 4, 1938.

v SYNGHRONOUS COMMUNICATION SYSTEM Filed May 22, 1955 8 sheets sheet 5PR/lYTER-\ l9 mvm'roR HARRY d. NI CHOLS ATTORNEY Jan. 4, 1938. H. J.NICHOLS SYNCHRONOUS COMMUNICATION SYSTEM Filed May 22, 1935 8Sheets-Sheet 6 cemen Dis 01a t Fi 12.

12v VENTOR HARRY J.NICHOLS. )ZTORA/E y Jan. 4, 1938. H 0 5 2,104,570

SYNCHRONOUS COMMUNICATION SYSTEM Filzd May 22, 1933 8 Sheets-Sheet 7 1NVEN TOR HARRY J. NICHU LS Jan. 4, 1938. H, J cHo s 2,104,570

SYNCHRONOUS COMMUNICATION SYSTEM Filed May 22, 1933 8 Sheets-Sheet 8Linc INVENTOR HARRY J. NICHOLS.

A TTOR/VEV Patented Jan. 4, 1938 UNITED STATES SYNCHRONOUS COMMUNICATIONSYSTEM Harry J. Nichols, Dayton, Ohio, assignor to InternationalBusiness Machines Corporation, New York, N. Y., a corporation of NewYork Application May 22, 1933, Serial No. 672,161

64. Claims.

-This invention relates to synchronous communication systems andparticularly to single impulse printing telegraph systems.

A general object of the invention is to provide a printing telegraphsystem in which single signal impulses, distinguished only in respect totime, are utilized to automatically establish synchronism, to providecontinuous phase correction to maintain synchronism, and to select theprinting characters and printing movements.

A more specific object is to provide a synchronizing and selectivesystem, and suit-able apparatus, whereby an electric typewriter. withminor modifications and changes, can be utilized as the printingmechanism of a printing telegraph.

A further object is to provide a printing telegraph system in which thegreater part of the apparatus is utilized for both sending and receivingfunctions with consequent advantages in economy and in simplification.

A further object is to provide a printing telegraph system in which bythe simple manipulation by the operator of a. single switch, theapparatus is instantly placed in the sending, receiving, or typingcondition.

A further object is to provide printing telegraph apparatus utilizing astandard typewriter key board and with both lower case and upper caseletters, figures, and characters, with auto- .matic operation ofcarriage return, shift, spacer, tabulator, and back spacer etc, so thattelegraphic communications may be transmitted in the form of the usualcommercial or personal letter.

A further object is to provide printing telegraph apparatus of thespeed, touch, and key board of a standard typewriter so that typiststrained to operate the ordinary typewriter may, Without specialtraining, operate the printing telegraph apparatus described in thepresent invention.

Afeature of the present invention is that the typewriter utilized as theprinting mechanism of the printing telegraph system herein disclosed,when not being used for the transmission or reception of messages, isequally suitable for typing letters. reports, etc. of the usual nature.

A further object of the present invention is a simple calling signallingarrangement whereby initial calls can be made whether or not the drivingmotor is running, and while the typewriter is being used for typing, andbreak-in calls can be made during transmission, the same apparatus beingutilized to effect calling signals under the several conditions.

A further object of the invention is to automatically establish andmaintain in a positive manner and with exactness, synchronism betweentransmitting and receiving apparatus at separate points.

A further object is to accomplish such synchronism by means of singleimpulses transmitted at a definite phase position during each cycle ofmotion of the transmitting apparatus.

A further object is to accomplish such synchronism by means of signalimpulses suitable for transmission over telephone, telegraph or radiocommunication systems without special adaptation of such systems.

A further object is to maintain close synchronism of the receivingapparatus by correcting, if necessary, and in the degree necessary, thephase position of the controlled element once during each cycle ofmotion, ensuring that the controlled element moves at all times in closesynchronism with the controlling element.

A further object is to provide a governor for driving motors for thesynchronized elements which is accurate, sensitive, and quick inresponse, and which is compensated for temperature efiects.

A further object is to provide a governor for the driving motor whichpermits minor speed adjustments to be made electrically withoutadjustment of the mechanical settings of the governor and withoutimpairing the range of operation and accuracy of regulation of thegovernor.

A further object is to provide a motor speed control arrangement wherebymeans operable from a distance may be utilized to effect a minoradjustment of the motor speed in a predetermined amount without loss ofcontrol by the governor.

A further object is to provide a synchronizing arrangement which bysimple switching methods is immediately convertible for eithercontrolling or controlled functioning.

A further object is to provide a particular form of electro-magneticrelay and associated circuit and apparatus whereby the relay may beoperated by a single current impulse of short duration, and is held inthe operated condition as.

long as similar periodic impulses are applied, and which resumes theunoperated condition when a single periodic impulse is missed. p

A further object is to provide a phase correcting mechanism which issimple in construction, accurate in operation, reliable and durable, andwhich automatically compensates for instrumental and line retardation ofsignals.

A further object is to provide a smooth acting phase corrector whichwhile in continuous operation, will not tend to change the speed of thecontrolled element when running in synchronism.

A further object is to provide an electro-magnetic phase corrector whichfunctions to correct the phase position of the controlled elementwithout physical engagement therewith.

A further object is to provide non-repeat means in the sending conditionwhereby only one signal is sent to the line for each operation of atype-bar key lever.

A further object is to provide interlock means whereby only one keylever may be depressed at a time. A further object is to provide keylatch and key release means whereby during sending operations, a keylever when depressed is retained in that position until the rotarydistributor collects the corresponding signal, whereupon the key leveris released for return to the unoperated position,

A further object is to provide means whereby the key latch is held outof engagement with the key levers after release by collection of thesignal, and thereafter as long as the key is held depressed manually,and is permitted to return to the position of engagement with all keylevers when the held key is released.

A further object is to provide automatic cutoif means for the electronicrelay whereby the-current impulses corresponding to the received signalimpulses are made of uniform duration irrespective of the duration ofthe signal impulses.

A further object is to provide duplex transmission means wherebybreak-in calls may be received when transmitting.

Other objects and features will be in part obvious and in parthereinafter pointed out in connection withthe following descriptiontaken in connection with the accompanying sheets of drawings formingpart of this disclosure.

In the drawings, Figs. 1A and 1B, which are to be considered as parts ofthe same drawing, show in diagrammatic form the circuits and apparatuswhich together with the typewriter or printer comprise a completecommunication unit. Fig. 1A shows the circuits and apparatus utilized insending, receiving, and calling. The circuits are shown in the typingcondition, which is the condition when the selector apparatus is notbeing used for sending and receiving, and the typewriter is availablefor typing. Fig. 1B shows the power rectifier providing power for thevarious relays, magnets, etc. comprising the selectingapparatus, and thedistributor driving motor and its control.

Fig. 2 shows in diagrammatic form the circuits and apparatus utilized insending, and for purposes of explanation is referred to as the sendingstation or station A.

Fig. 3 is a similar diagram of the circuits and apparatus utilized inreceiving, and is referred to as the receiving station or station E.

Fig. 4 is a similar diagram of the circuits and apparatus used incalling.

Fig. 5 is a plan view of the rotary distributor assembly including theplateau with segments and ring, the rotating distributor arm, and thecorrector magnet in relation to the distributor, showing thedistributor. arm in the rest position preparatory for release toestablish synchronism.

Fig. 6 is a side view, partly in section, showing the same assembly asin Fig. 5, and details of the hub, drive shaft, and friction drive.

Fig. 7 is a sectional view on line VII-VII of Fig. 6, looking towardsthe corrector magnet.

Fig. 8 is a side view showing a modification of the correctorarrangement, in which the corrector bar passes across the face of thecorreotor magnet poles.

Fig. 9 is a plan view of the structure shown in Fig. 8.

Fig. 10 is a side view showing a further modification of the correctorarrangement.

Fig. 11 is a side perspective viewof the corrector bar shown in Fig. 10.

Fig. 12 is a pull-displacement diagram showing the general nature of thetangential magnetic pull on the corrector bar by the corrector magnet.

Fig 13 is a plan view of the electro-magnetic clutch arrangement shownin the rest position.

Fig. 14 is a similar view, omitting the clutch magnet, and showing theclutch cam position for free rotation of the distributor hub.

Fig. 15 is a side view of the .cam mechanism assembly shown in Fig. 14.

Fig. 16 is a cross sectional View of the clutch cam taken on lineXVI-.-XVI of Fig. 13.

Fig. 17 is a schematic circuit diagram, showing the part of the circuitassociated with the clutch relay magnet.

Fig. 18 is an end view of the governor assembly.

Fig. 19 is a side view of the governor assembly.

Fig. 20 shows, in exaggerated form, the efieot of temperature on thethermal compensation means for the governor.

Fig. 21 is a diagram showing schematically the arrangement for minoradjustment of the motor speed.

Fig. 22 is a fragmentary view of the key interlock, illustrating theprinciple of operation.

Fig. 23 is a side view, partly in section, of the solenoid assembly, thekey interlock, and the key latch, showing the construction andarrangement of these parts. The spring link for connecting the plungersof the solenoids to the members which they actuate is also shown.

Fig. 24 shows the left end of the space bar assembly, showing thedetails of construction.

Like characters represent like parts.

General description A complete installation unit consists of an electrictypewriter, a typewriter control assembly, and a. distributor unitassembly. The typewriter control assembly is mounted underneath andinside the typewriter frame. The distributor unit assembly is housed ina case, and is located near the typewriter. The two assemblies areconnected electrically by a multiple conductor cable.

The principal items of equipment comprising a typewriter controlassembly are:

(a) The key solenoid assembly.

(b) The key switches.

(c) The auxiliary switch.

(d) The key latch.

(e) The key latch release magnet.

(f) The key interlock.

(g) The send-receive switch.

The principal items of equipment comprising a distributor assembly are:

(a) The rotary distributor.

(b) The drive motor.

(0) The rectifier.

(d) The clutch mechanism.

( e) The phase-Corrector arrangement.

(1) The electronic relay.

(0) The cut-off relay.

(h) The non-repeat relay.

(1') The duplex transmission arrangement.

(7') The call circuit.

(k) The multiple switch relay.

In Fig. 1A, the apparatus comprising the typewriter control assembly isincluded within the dot-dash rectangle. cluded in the distributor unit.

All other apparatus is in- The apparatus shown in Fig. 1A performs thefunctions of transmitting and receiving printing impulses andsynchronizing impulses, both, of which classes of impulses aredistributed via the rotary distributor. Referring to Figs. 1, 5, 6, therotary'distributorconsists of a series of metallic segments II, andsolid metallic ring I2, both mounted on a disc I4 of insulatingmaterial, and the rotary brush arm I3, rotatably mounted on andyieldingly driven by the drive shaft 55. The ring and segments, whileactually arranged in concentric circles, are shown in linear developmentin some figures in order to simplify the diagram. The rotary brush armI3, which makes electrical connection from ring to segments, passesacross all the segments once dur-.

ing each revolution in a well understood manner. The drive shaft 55 isconveniently driven at uniform speed by a motor 99, as hereinafterdescribed. The brush arm I3 is shown in the rest position on segment 3.

A clutch release relay I5 is provided to stop and to release the brusharm in accordance with the invention, and for illustrative purposes isshown with its armature IS in engagement with the brush arm I3. The"armature I6, also actuates springs I! and I8 which function inconnection with receiving operations.

The release relay I5 is provided with a low impedance winding and a highimpedance winding 2| connected in series. Across the terminals of thewinding 2| is connected 2. storing condenser 22. The outer terminal ofthe winding 20 is connected to the positive bus the outer terminal ofwinding 2| is connected to spring I8, to spring I92 of the send-receiveswitch I90, and to one terminal of the corrector magnet 36. The releaserelay I5 is of the quick-acting, slow release type, and responds quicklyto a short current impulse, but holds for a prolonged period, and ifsupplied with properly timed impulses continues to hold in the operatedposition as long as such impulses are regularly received. A relay whichso operates is sometimes called a pulse sustained relay, and while otherforms of such relays are in use, the particular form here disclosed isnovel and constitutes part of the present invention. It is described infurther detail hereinafter.

The power for transmission purposes and for the operation of the variousrelays and magnets is obtained from any suitable direct current source.preferably from the rectifier assembly shown in Fig. 1B. The rectifierassembly consists of the power transformer 2K9, rectifier tube 2|I,-preferably of full-wave type as shown, the filter condenser '2I2, andfilter choke 2I3, all connected as shown. The power transformer 2H] hasa primary 2 I4, connected" to the power mains 2H; secondary 2I5 tosupply heating current to the cathode of tube 2| I center tappedsecondary 2I6 to supply anode current to the tube 2H; and secondary I37with center tap I36 to supply heating current to the cathode of theelectronic relay I32.

The output of the rectifier is applied to the terminals of the voltagedivider 24a and 24?) shown in Fig. 1A. The positive bus 25 is connectedto the positive terminal of the voltage divider, and the negative bus 26to the negative terminal. The zero bus |3| is connected to the zeroterminal between sections 24a and 24b of the voltage divider, thesection 24b thus furnishing in a well understood manner a negative biasfor the grid I33 of the electronic relay I32.

The elements of the electronic relay I32, which is of the gridcontrolled, gaseous discharge type are the grid I33, the cathode I34 andthe anode or plate I35, all contained in an evacuated glass envelope, asis well understood. Th/E center tap I36 of the cathode heatingtransformer I3! is connected to the zero bus I3I.

In series with the plate I of electronic relay I32 is the cut-off relayI10, connected as shown, with winding I'Il shunted by variable resistorI12, and provided with contacts I13 and I14. As is. well known, the gridof a grid controlled gaseous discharge tube is usually unable to stopthe discharge when once started, and the plate current is normally cutoff by disconnecting the plate supply, or by causing the plate to becomenegative in respect to the cathode. While either method may be used, itis preferred in the present case to cut off the plate current after ashort interval by utilizing the cut-off relay to open the contacts I'i3|I4. The variable resistor I12 permits of very exact timing of thecut-off interval, and the whole arrangement is rugged and reliable. Aspark suppressor arrangement may be connected across the contactsII3-I'I4 to reduce sparking to a negligible degree.

The duplex transmission arrangement consists of the sending or outputtransformer 21 with primary winding 23 and secondary winding 29; and thereceiving or input transformer 32 with center tapped primary 33 andsecondary 34. The resistor 35, of a suitable value to balance the lineimpedance, is connected across the secondary 34, and across thisresistor 35 appears the potential which overloalances the normal bias onthe grid I33, and trips off the electronic relay in a well understoodmanner. The center tap of the primary 33 is connected to one terminal ofthe secondary 29, the other terminal being connected to the lineterminal 39.

One terminal of the primary 33 is connected to the terminal 30 while theother terminal is connected to line terminal 3| thru the artificial linenetwork A. L. as shown.- The functioning of duplex transmission beingwell understood, the operation is manifest, and does not requirediscussion beyond that which will be given hereafter in connection withthe calling circuits.

The send-receive switch I90 is a three position switch, the threepositions being indicated by R. T. S. referring respectively to thereceiving, typing, and sending conditions. The switch is of the levertype and has one "set of break-make springs, and one set of makesprings. These springs are numbered from 191 to 195 inclusive. In the Tand S positions, the send-receive switch mechanically holds theuniversal bar key latch I5I out of engagement with the key levers I56.

The multiple switch relay I60, controlled by the send-receive switch I90, provides the automatic switching operations required to change fromsending condition to receiving condition and vice versa. It is providedwith a single winding I6I, and three sets of break-make contactsnumbered from 1 to 9 inclusive. In order to simplify the diagram, thesecontacts are shown in their natural locations in the circuit, and arenumbered 1 to 9 inclusive for the purpose of identification. In serieswith the Winding IGI is the reading condenser arrangement comprisingcondenser I62 and shunt resistor I63. of the reading condenserarrangement, as is well understood in the art, is to provide a strongoper- The purpose ating pulse in the circuit followed by a lower holdingcurrent. It also compensates in part the inductance of the circuit ofwhich it is a part.

Synchronization Referring to Fig. 2, the transmission of synchrom'zingimpulses is accomplished as follows:

Assume that the brush arm I3 is frictionally driven, but is held in therest position on segment 3 by the armature I6 of the relay I5. To startsending synchronizing signals, the send-receive switch I90 is thrown tothe S position, as indicated. This completes a circuit from zero busthru reading condenser I62 thru winding I6I of ls multiple switch relayvia contacts I 9I-I92'of send-receive switch to relay I5, thru condenser22 and winding 20 to positive bus. A strong cur-- rent thru this circuitoperates multiple switch relay I60, breaking contacts 2--3, 56, 6-9 andmaking contacts I2, 4-5, 1-8. Release relay I5 is also energized,attracting armature I6 which releases brush arm I3. As condensers 22 andI62 become charged, a small steady current limited by resistor I63 fiowsthru windings I6I and 2| providing sufficient holding current to holdthe multiple switch relay and release relay in the operated condition. Astrong operating pulse followed by low holding current is thus provided,preventing over heating of the relay windings.

On being released by armature I6, the brush arm I3 is set in rotation bythe friction drive,

and takes up the uniform speed of the drive shaft set by the drivingmotor. When the brush arm reaches segment I, a circuit is completed frompositive bus via contacts 8-1 thru the pulse shaping net-work comprisingthe reading condenser I65 and shunt resistor I66 and inductance I61 inseries therewith, via contacts 45 to segment I, via brush arm l3 to ringI2, via contacts 2I thru primary 28 to zero bus. For the duration of thecontact of the brushes with segment I, current flows thru the circuitjust traced, and a corresponding signal impulse is sent to the line bythe secondary 29 of the output transformer 21. This impulse, which isrepeated for each revolution of the brush arm I3, is called thesynchronizing signal.

It is to be noted that the synchronizing signal in its passage to theline from secondary 29 passes thru primary 33 via the center tap, andthus thru the equal sections of primary 33 to the line terminals. Withthe artificial line A. L. in proper balance the currents thru thesections of primary 33 are equal, and in opposition, hence no voltage isinduced in the secondary 34 and the grid I33 is unaffected by signalssent to the line under these conditions.

Referring to Fig. 3, the reception and application of the synchronizingsignals at the receiving station is as follows:

At the receiving stati0n,'the synchronizing signals are received at theline terminals 30 and 3! and are applied to the terminals of primary 33of the input transformer 32. The current from terminal 30 passing thruthe secondary 29 of the vfully described hereinafter.

ducting, and current flows in the plate circuit. The brush arm I3 beingat rest on segment 3, a circuit is completed from zero bus thru centertap I36, and transformer winding I31 thru cathode I'34 to plate I35 viacontacts I13I14 thru winding I1I via contacts I94-'I95 of thesendreceive switch and contacts 32 to ring, via. brush arm I3 to segment3 via contacts I1--I8 thru condenser 22, thru winding '20 to positivebus. A strongcurrent pulse flows thru this circuit, operating releaserelay I5 and thereafter cutoff relay I10, which opens contacts I13--I14, terminating the pulse. The armature I6 is pulled in, releasing thebrush arm I3, and opening contacts I 1I 8. The flow of current thrucondenser 22 has charged that condenser providing holding current forthe high impedance winding 2|, delaying the release of armature I6. Thecut-off relay I10 releases quickly, being of low impedance, and beingshunted by the resistor I12. Before relay I10 closes its contacts,however, the plate current has been interrupted long enough to permitthe electronic relay I32 to de-ionize and the grid I33 to regaincontrol. The electronic relay I 32, with its associated cut-off relay,thus provides strong local current impulses which are initiated by theline-signals, but which are of definite duration.

When released, the brush arm I3 is set in motion by its friction drive(and clutch as is explained hereinafter) and-is thereafter rotated atuniform speed. Brush arm I3 having started starting the brush arm fromrest on segment 3 enables the brush arm to arrive at segment I as thenext synchronizing signal is received. The

synchronizing signal energizes the electronic re- I lay I32 as before,but this time the circuit. is com pleted via segment I as follows: viasame circuit as before to ring, via brush arm to segment I, via

contacts. 56, thru winding of corrector magnet 36, thru condenser 22 andwinding 20 to positive bus. The current pulse thru this circuitreplenishes the charge on condenser 22, maintainingthe release relay I5in the operated condition, and energizes the corrector magnet 36. Thedetails of the operation of the corrector magnet 36 and release relay I5will be more At this point it is to be observed that provided the brusharm I3 arrives on segment I when the synchronizing signal is beingapplied to the grid of the electronic relay, the charge on the condenser22 is replenished, sustaining the'operation of the release relay I5, andthe corrector magnet 36 is energized. If these conditions are notfulfilled, release relay I5 drops out, and during the subsequentrevolution the brush arm I3 is stopped on the rest segment. If thesignals continue, the same procedure is repeated until synchronism isestablished.

In practice, itis found that with proper adjustment of the clutchmechanism and by setting the rest position for the brush arm at theproper place, synchronismis usually established on the first revolution.Thereafter, synchronism is maintained by the corrector magnet correctingthe phase angle of the receiving distributor arm to keep it in unisonwith the sending distributor arm. Should, for any reason, unison withinapproximately one half segment width be departed from, the brush arm I3is stopped on the rest segment by reason of release relay I droppingout, and the synchronizing procedure is repeated when the nextsynchronizing pulse is received. Thus synchronism, if lost, is automatically re-established.

Sending circuits and operations Referring to Fig. 2, the printing signalimpulse transmitting apparatus includes the key switches I51 ofbreak-make type, one for each key of the typewriter, there being 48 keyson a standard typewriter key board. The armature spring of eachkey-switch is connected to an individual segment; the make springs areconnected to the common key-switch bus I38, as shown. The keyswitch busis connected to one terminal of the non-repeat relay I40, and to spring144 of relay I40.

Each key lever operates its associated keyswitch by means of aninsulated push rod I50 as indicated. For transmitting purposes, each keylever when depressed is held down by the universal bar key latch I5Iuntil released by the key release magnet I52. The universal bail I53 ispositioned below and transversely across the row of key levers, beingheld in light contact therewith by a retractile spring (not shown). Whenany key is depressed, the bail I53 closes the auxiliary switch I54 bymeans of push rod I55. One spring of the auxiliary switch is connectedto the key switch bus I38; the other spring is connected to spring I42of non-repeat relay I40.

The non-repeat relay I40 has a low impedance winding I45, located on theheel end of the core I40, and a high impedance winding I41. In serieswith the winding I41 is aweading condenser arrangement consisting of thecondenser I48 and shunt resistance I49.

To commence sending, the send-receive switch is thrown to the Sposition, and synchronizing signals are sent to the line for a fewseconds to permit the receiving machine to come to synchronisrn asdescribed above. Printing signals may then be sent by depressing thetypewriter keys as for ordinary typing.

Assuming key 5 to be depressed, the operations which result are asfollows: As the key lever nears thebottom of its stroke, the mechanismof the typewriter is tripped, and the typewriter immediately types theselected character to furnish a local copy of the message. The key leveris latched down in the depressed position by the universal bar key latchI5I hooking over the end of the key lever I50. The finger can be at onceremoved from the key. When the key is pressed down, the push rod I50(one for each key lever) which abuts against the lower edge of the keylever, pushes down the armature spring of its associated key switch,breaking the upper contacts and making the lower contacts. The universalbail I53 is also rotated about its axis by the movement of the keylever, and operates the single push rod I55 which closes the auxiliaryswitch contacts. The operation of the key switch connects the key switchbus I38 to the segment associated with the particular key switch, in thepresent instance segment 5. 'When the brush arm I3 arrives at segment 5,a circuit is completed from positive bus, via contacts 8-1 thru lowimpedance winding MS of non-repeat relay I40,'via contacts I4 2-I45 tokey switch bus B8,

viamiddle andlower contacts of the operated key switch to segment 5, viabrush arm I3 to ring, via contacts 2-I thru primary 28 of outputtransformer 21 to zero bus I3!. A strong current impulse flows thru thiscircuit, its duration being determined by the time of contact of thebrush arm I3 with segment 5, and a printing signal of the same durationis sent to the line by the secondary 29 of the output transformer 21.

Non-repeat and key release arrangement The local current impulse justdescribed, in addition to sending a printing signal to the line, alsoperforms an important part in the nonrepeat and key release actions. Thelocal current pulse thru winding I46 of non-repeat rclay I40, togetherwith the part of the pulse flowing thru the high impedance winding I41,operates non-repeat relay I40, thus opening contacts I44--I45, andclosing contacts I44-I43, and I42--I4I. Opening contacts I44I45 cuts offthe winding I46. Closing contacts I44-I43 connects one terminal of thekey release solenoid I52 to the key switch bus I38 and to winding I41.Closing contacts I42I4I connects the zero bus I3I to the upper spring ofthe auxiliary switch and thru its contacts places zero potential on thekey switch bus I38. Any connected segment, except the synchronizingsegment, is therefore likewise placed at zero potential and no moreprinting signals can be sent to the line. This constitutes thenon-repeat feature.

Closing contacts I42-I4I also completes a circuit from negative bus viacontacts I4I-I42, via contacts of the auxiliary switch, thru winding I41and reading condenser I48 via contacts 8-1 to positive bus. Current thruthis circuit re-energizes non-repeat relay I40 and supplies'holdingcurrent therefor. A second circuit is completed from positive bus viacontacts 8-1 thru the winding of the key release solenoid I52, thrureading condenser I18 via contacts I43--I44, via auxiliary switch.contacts, via contacts I42- IM to zero bus. A current pulse thru thiscircuit energizes the key release solenoid I 52, whose plunger pulls thekey latch I5I away from the key levers by means of the extension I82 asshown.

If the finger is removed from the freed key, the key lever is drawn upby its retractile spring and the springs of the auxiliary switch I54lift the push rod I55 and open the contacts.

Opening these contacts breaks the circuit to zero bus via contactsI42-I4I, and takes the holding current from the non-repeat relay I40 andkey release solenoid I52, which thereupon release. Zero potential isalso removed from the key switch bus I38 and any connected segment. Whenthe key release solenoid I52 releases, the key latch I5I is returned toan engageable position by the retractile spring I83. When the nonrepeatI40 releases, contacts I4I-I43 and 143- I44 are opened, and contactsI44--I45 are closed, restoring initial conditions.

It is to be noted the non-repeat relay I40 and key release solenoid I52are not released until the contacts of auxiliary switch I54 are allowedto open. Consequently, should a key be deliberately held down, repeatsignals are not permitted to be sent to the line, and the key latch isheld out of engagement until the key is released. The result is thatonly one signal can be sent to the line for each depression of a key,and the time key is held down is of no consequence as regards theoperation of the apparatus nor as regards the accuracy of transmission,In normal operation the keys are depressed and released quickly by theoperator, and are released by the key-release solenoid practicallyinstantaneously when the printing signal is sent to the line.

Key interlock It will be apparent from the foregoing description ofsending operations, that a variable interval intervenes between theclosing of a key switch and the collection of the impulse from theconnected segment by the distributor brush. This interval depends on thespeed at which the distributor rotates and the angular travel of thebrush arm inorder to reach the connected segment, the interval beingalways less than the time of one revolution.

.It is manifest that if two keys were pressed simultaneously, or almostsimultaneously, the distributor would send out a printing signal fromthe first connected segment, whether or not this was the proper orderfor transmission. To eliminate errors of this kind; a key interlock isprovided which permits only one key at a time to be depressed. Whilevarious forms of interlock have been devised and employed, the preferredform is shown in Figs. 22 and 23. This form of interlock is well known,and its operation being familiar to those current with the art, detaileddescription is not required.

The principal parts of the interlock are the comb 235, the roller race234, and the rollers 236, one for each key lever plus one. Each keylever is located in an individual slot in the comb 235 as shown. Thediameter of the rollers is exactly equal o the key space centers, andthe space between all the rollers combined is slightly greater than thethickness of a key lever I56. As indicated in Fig. 22, when one keylever is depressed, the slots for all the rest of the key levers areblocked.

Dual space segment arrangement With a single impulse system as hereindescribed, the duration of the signal impulse is determined by thenumber of segments on the distributor and the speed of rotation of thedistributor arm.

There is a practical lower limit to the duration of the signal impulse,since the shorter the impulse, the higher the required frequencycharacteristics of the transmission system connecting the sending andreceiving stations. As is well known, all communication systems havedefinite limits as to frequency characteristics, the limits beingparticularly restricted on telegraph cable circuits. One of thelimitations on the speed of operation of printing telegraph systems istherefore the length of the signal impulses and the number of segmentson the distributor and the speed of rotation of the distributor arm aresubject to this and other limitations.

One of the features of the present invention is the means by which thenumber of words transmitted in a given time is increased without amaterial shortening of the signal impulse. An average word intelegraphic practice consists of five letters and a space, and the speedof transmission is rated on the basis of the number of equivalentaverage words sent per minute. On the average, since a space occurs forevery five letters, one sixth of the signals are space signals. In thepresent invention, means are provided whereby the average time requiredto collect and transmit a space signal is approximately 2 one half. thatrequired to collect and transmit other printing signals. The means is toprovide two segments for the space signal located approximatelydiametrically opposite on the distributor. These segments are connectedin parallel, and either one can transmit or receive a space signal. Thearrangement is indicated by the connection of segments 8 and 38 in Fig.1A. Thus, when the space bar is depressed, the distributor arm on theaverage moves only one quarter revolution until the signal is collected;for other signals an average movement of one half a revolution isrequired. As an example of the advantage of this improvement, assumethat the distributor arm makes 4 revolutions per second. The theoreticalaverage speed of transmission, using only one space segment, would be:

words per minute. Using the dual space segment arrangement, thetheoretical average speed would be:

words per minute (approx.).

Sine wave impulse feature divider 24a and in series with section 241),to-.

gether with wave shaping arrangements and proper design of the circuitconstants of inductance, resistance, and capacity. In the sendingcircuit connected to segment I for generating synchronizing impulses,the wave shaping arrangement comprising the reading condenser I andshunt resistor I66, and inductance I65, in series therewith, togetherwith the storage condenser I86 and the primary 28 of the outputtransformer 21, co-operate to produce a sine wave impulse in thiscircuit, and virtual sine wave synchronizing signals are sent to theline. In

.the printing signal circuits, the storage condenser I86, the readingcondenser I48, windings I46 and I4! of non-repeat relay I40, and theprimary 28 co-operate to produce sine wave impulses in these circuits.

Receiving circuits and operations Synchronism having been established aspreviously described, and the brush arms at the receiving and sendingstations being in unison, printing signals may be sent to the receivingstation as described in connection with sending operations.

Referring to Fig. 3, the printing signals when received are impressed onthe primary 33 of the input transformer 32, and potential variationsfrom the secondary 34 cause a drop across resistor 35 opposing thenegative bias on grid I33 which on becoming sufiiciently positivetriggers off the electronic relay I32, which becomes conducting. Acircuit is thus completed from zero bus I3I thru center tap I35, andwinding I31,

from cathode I34 to anode I35, via contacts I13-I14 thru winding I1I,via contacts I94-I95, via contacts 32 to ring, viabrush arm I3 to theparticular segment with which the brushes of distributor arm I3 are incontact.

I segment, of which segment 5 may be considered as an example, thecircuit continues via the middle and upper contacts of key switch I51 towinding I59 of key magnet I58 to key magnet bus I39, thence via contacts8-9 to positive bus 25. The pulse thru this circuit energizes cut-offrelay I10 and key magnet I58, whose plunger is attracted, stretchingspring link I84 which pulls down the key lever to which it is attached.The key lever trips the typewriter mechanism (not shown) and thecharacter is printed. As the key lever nears the end of its downwardtravel,'the push rod. I50 breaks the middle and upper key switchcontacts. Owing to the inductance of the key magnet, the inertia of theplunger and the key lever, and the action of the springlink I84, thebreaking of the key switch contacts is retarded and the circuit isactually broken by the opening of the contacts I13-I14 by the cut-offrelay I10. The length of the printing impulses and the synchronizingimpulses is thus determined by the setting of the cut-off relay I10, andthis relay is in practice adjusted to cut-off shortly before thetermination of, the line signal.

From this i In this way, the circuit is normally broken at g contactsI13-I14, which may be provided with a spark suppressor arrangement tosuppress sparking at these contacts. With perfect unison, the circuit isbroken before the brushes leave the connected segment, hence sparking atthe distributor is minimized, such sparking as occurs being principallydue to the inductive energy in the key magnet. The sparking at thecontacts of the key switches is negligible.

It is to be observed that when receiving printing signals, the keymagnet energized is that which is connected to the segment beingcontacted by brush arm I3. When the brush'arms at the sending andreceiving stations are in unison, the key magnet selected at thereceiving station will correspond with the key switch-closed at thereceiving station. Accuracy in selection thus depends on close unison ofthe brush arms, and cutting off the printing impulse before the brusharm at the receiving station has carried over into contact with theadjacent segment. The corrector magnet provides the required closeunison, and the cut-oil relay terminates the impulses, bothsynchronizing and printing, after a definite interval. The cut-ofi relaythus enables the printer mechanism to clear one operation before asucceeding operation is initiated. The line retardation and ionizingtime of the elec tronic relay are not material factors with the presentinvention, since the synchronizing signals are subject to the same delayas are the printing signals, and the corrector magnet automaticallycompensates for this delay. Likewise,

any instrumental delays from line relays, etc.

interposed in the transmission system are automatically compensated for.

While for illustrative purposes, the sending and receiving stations arerepresented as being connected by a transmission line consisting. of oneimportant factor in its ready adaptation to various forms ofcommunication circuits.

circuits separated from the other circuits, the

apparatus receiving the calling signals from the line include theartificial line A. 'L., and the primary 33 of the input transformer 32..The apparatus for utilizing the calling signals comprise the secondary34 of the input transformer, the glow lamp 202, the electronic relayI32, the cut-out relay I10, the send-receive switch I90, and thecallbell 20I. The send-receive switch I controls the calling circuit.When the sendreceive switch is in either the typing or sendingpositions, the call bell is connected in the calling circuit; when thesendareceive switch is in the receiving position, the call bell isdisconnected.

Assume that the send-receive switch at the receiving station is in thetyping position and that the machine is being used for typing purposes.To call, the sending station throws the sendreceive' switch to the Sposition and sends synchronizing signals to the line as described undersynchronization. From terminals 30--3I of the receiving station, thesignals traverse the circuit from terminal 30 thru primary 33 thruartificial. line A L. to terminal 3|. Some current flows thru secondary29, but the primary 2B is open, and this current is inefiective. Thesignal ing I1,I of cut-01f relay I10, via contacts I94-I93 thru windingof the call bell20l to positive bus 25. Current flowing in this circuitenergizes the" call bell, and also cut-off relay I10, which oper atesand breaks the circuit in the usual way. I

This action is repeated as each synchronizing impulse is received. Sincethe cut-oil relay opens the circuit after each pulse, the interrupter inthe bell can be dispensed with.

To stop the bell, the send-receive switch is thrown to the receiveposition which opens the calling circuit, and establishes the receivingcircuit as shown in Fig. 3. The receiving distributor is thensynchronized, as previously described, and transmission begins.

The second calling situation is that existing when a station is sendingand the receiving station wishes for some reason to call back. This isthe so called break-in call. Referring to Figs. 2 and 3, the circuitconditions at the sending station are shown in Fig. 2, those at thereceiving station in Fig. 3. To make the breakin signal, the receivingstation throws the sendreceive switch to the send position, changing itscircuit conditions to those shown in Fig. 2, and synchronizing signalsare immediately sent to the line in the reverse direction, i. e. fromreceiving station to sending station. The calling circuit at the sendingstation is in the condition shown in Fig.- 4, the send-receive switchbeing in the position shown by dotted lines. Due to the duplexarrangement of the transformers, previously described, the receivedsynchronizing signals actuate the electronic relay I32, and-the callbell is energized as previously described. Due to the going signals donot actuate the electronic relay.

Without further analysis, it will be evident that a called station canacknowledge the call,and signal ready, by throwing the send-receiveswitch momentarily to' the send position in answering a call, and beforemoving to the receive position. The calling station is thus informed ofthe readiness of the called station, and can start sending withoutdelay. I

In the foregoing, the call signal device was described as a bell. It isobvious, however, that any of the usual audible or visual signallingdevices, such as buzzers, gongs, annunciators, lamps, etc. can beemployed, the power in the calling circuit being adequate for operatingsuch devices and such variations are included within the scope of theinvention as defined by the generic claims. I

It will be observed that in the foregoing de scription of the callingsystem, two way communication circuits were assumed. When one waycircuits, such as radio circuits, are employed, break-in and call-backsignals are not usually feasible and the usual calling conventions forone way circuits must be observed;

It is further to be observed that with the calling system described, itis not necessary that the distributor motor be turned on, but that powermust be supplied to the electronic relay. To receive a calling signalwithout having, power on the electronic relay, a smallneon glow lamp 202is connected into the calling circuit at some convenie'ntpoint, as forexample across the sec ondary 35 as indicated in Fig. 4.

It will be perceived that I have provided a simple and flexible callingsystem which is very economical in cost, and which possesses numerousadvantages.

The electronic relay The electronic relay I32 may be of the hotcathodetype, as shown, or of the cold cathode type, in which case the cathodeheating transformer I3! is not required. As is well known, the gridpotentials sufiicing to ionize electronic relays is comparatively low,and they are therefore susceptible to stray potentials, inductiveeffects, etc. and for best results, measures to insure stability inoperation are desirable. In the present invention, stabilizing measureswhich have been found eifective comprise the grid current limitingresistor 203, the grid to cathode by-pass condenser 204, and-the gridpotential stabilizer arrangement consisting of the ballast condenser 205and the ballast resistor 206.

The function of the current limiting resistor 203-is to limit the gridcurrent to moderate amounts during the periods when the grid ispositive. It is preferably of a comparatively high value, values of50,000 to 500,000 ohms giving good results. The function of the grid tocathode by-pass condenser 204 is to by-pass high frequency andinductivepotentials, preventing ionization of the relay from these effects. Thiscondenser may be of comparatively small size, capacities of the order of.0025 mid. having been found to give good results.

The function of the ballast condenser 205 and ballast resistor 206 is topreserve uniform bias potentials on the grid I33. When local impulsesoccur, part of the charge on. storage condenser I86 is lost, and currentflowing thru bias reslstor 24b to replenish the charge on condenser i88causes a momentary variation in drop across balancing effect of theartificial line, the out- 2417. The potential across ballast condenser205, and consequently the grid bias potential, remain almost constantduring such variations, since because of ballast resistor 206, anychange in the charge on condenser 205 is retarded. The time constant ofthe combination of condenser 205 and resistor 206 is proportional to theproduct of their values, hence a wide range of values is possible. Thearrangement permits an electronic relay to be operated from a voltagedivider of momentarily fluctuating voltage with practically the samestability as is obtained with a battery to supply bias to the grid ofthe relay.

The rotary distributor and phase corrector In Figs. and 6, which show indetail the rotary distributor and corrector magnet assemblies, therotary distributor is seen to consist of a hub 31, with diametrallypositioned contactor arm 38 and corrector arm 39 mounted in cross holes4-0 therein by suitable holding means such as set screws 4|. On thecontactor arm 38 is mounted a link 42 of insulating material by means ofscrew 43, extending axially into the outer end of contactor arm 38. Onthe projecting end of link 42 is mounted the brush arm l3 by means of ascrew 44, extending axially into arm 13. The outer end of the arm I3 iscut into half-cylindrical section, and on the cut section is mounted thehalf-cylindrical brush clamp 45. Between the fiat surfaces of arm I3 andclamp 45 are clamped two flexible metallic brushes 40 by means of ascrew 41. The outer endsof the brushes 46 slope rearwardly and contactthe segments H and ring l2 with a light pressure; The brushes areconveniently made of copper braid, bundles of small copper wires, orsilver strips, as iscommonly practiced in the telegraphic art. 7

The corrector arm 39 carries at its outer end the corrector bar 49 ofmagnetic material, preferably a metal or alloy of low magneticpermeability such as soft pure iron, or magnetic nickel alloy. Thecorrector bar may have a variety of shapes, the preferred shape beingshown in Figs. 6 and 7. The corrector bar should be rigidly mounted onthe corrector arm, and is so mounted conveniently by positioning in aslot cut in the end of the corrector arm, and secured therein by one ormore screws 48 (one being shown) as clearly indicated. In the preferredform, the location and length of the cor rector'bar 49 is such that onrotation of the distributor hub, the corrector bar passes end-wisebetween the pole pieces 50 with a small air-gap at each end. The air-gapwhich has been found preferable is of the order of .025 inch.

The corrector magnet 36 is preferably mounted on a bracket 52,adjustable in an are by means of curved slots 53 and screws 54, so thatthe poles 50 of the corrector magnet 36 may be adjustable sidewiseconcentrically with the drive shaft 55. By this adjustment, thecorrector magnet 36 may be moved in relation to the synchronizingsegment I. will be evident when it is considered that a small intervalof time is required for the flux in the corrector magnet 38 to build upin response to the synchronizing current impulses, this interval in partdepending upon the inductance in the corrector magnet circuit. Duringthis small inter val, the distributor arm moves in the direction ofrotation, hence the corrector magnet for proper action should bedisplaced angularly in the same direction by a slight amount in excessThe need for this adjustment of the mechanical angle of 180 representedby the axis of the corrector arm and the line of contact of the brushes46. Thebest adjustment of the position oi. the corrector magnet 35 isreadily determined by trial and may thereafter be left fixed.

The best proportions for the faces of the poles of the corrector magnet,and for the corrector bar, may be in part determined by analysis, butrefinement in the design of these parts is most readily obtained byexperiment. The result desired is that the corrector bar should passbetween the poles of the corrector magnet without material retardationor acceleration when the distributor arm is in perfectsynchronism withthat of the sending station, but shall be subject to corrective actionwhen the synchronous relation is departed from.

Figs. 8 and 9 show a modification of the corrector bar-corrector magnetarrangement, in which the corrector bar 49 passes in front of the poles50 of the corrector magnet 36. The poles 50 are in this case narrowed atthe face nearest the corrector bar to substantially the width of thecorrector bar, as shown. On analysis, it will be evident that as thecorrector bar approaches ordeparts from the .poles 50, a tangentialmagnetic pull will be exerted. The correcting action will therefore bethe same as for the forms shown in Figs.6 and 7. The strong radial pull,however, requires increased rigidity for the drive shaft, to resist thisunbalanced pull. This unbalanced radial pull, together with the factthat the corrector bar 49 of the form shown in Figs. 8 and 9 is for thesame magnetic emciency heavier than that shown in Figs. 6 and 7represent comparative disadvantages for the first named type.

Another possible modification of the form of the corrector bar andcorrector magnet poles is shown in Figs. 10 and 11. Since thismodification represents a combination of those previously discussed, itsaction is'manifest and further dis cussion is unnecessary.

Various other combinations of pole pieces and corrector bar shapes arepossible, and such variations are included within the scope of theinvention as defined by the generic claims.

Fig. 12 shows a typical tangential magnetic pull-displacement curve. Theordinates represent, in arbitrary units, the tangential component of themagnetic attraction of the poles 50 on the corrector bar 49 shown inFigs. 6 and '7. The abscissae represent the displacement of the verticalmedian plane of the corrector bar from the median plane of the correctormagnet poles. The arrows within the diagramindicate that the pull istowards the median plane of the corrector magnet. From this curve it isevident that a tangential force tends to hold the corrector bar inalignment with the corrector magnet poles. Assuming the corrector magnetto be energized by uniform direct current, this force depends on theamount of the displacement of the corrector bar from the median plane ofthe corrector'poles,

and clearly indicates the nature of the corrective action of the.corrector magnet. "The curve shown is a static curve at a particularvalue of current. Other values of current produce a family of curves ofthe same general form. when the corrector bar is passed rapidly betweenthe poles, some distortion of the curve doubtless occurs. Also, thesynchronizing current impulse is of a general sine-wave form, causing arise and fall in the magnetizing force of the magnet. Practicalexperience indicates, however, that the curve shown in Fig. 12represents substantially the corrective action of the corrector magneton the corrector bar to maintain the latter in unison with the sendingdistributor arm.

Referring to Fig. 6 which shows details of the drive-shaft'hub assembly,the hub 31. preferably made of a light metal such as aluminum, has acylindrical axial bore 56 fitted to give a free turning fit on the driveshaft 55. A drive collar 51 is fixed on the drive shaft 55 by suitableadjustment means such as the set screw 58. To the periphery of thecollar 51 is cemented or vulcanized a rubber roll 59. Next is placedover the drive shaft a washer 6|, preferably of steel. Upon this washerrests the hub collar 62, to which is cemented or vulcanized the rubberroll 63. The hub collar 62 has an upwardly extending annular sectionwhich extends into a counter-bored cylindrical cavity in the lower endof the hub 31, and is adjustably secured therein by any preferred means,as by the set screw 64. Assembled on the hub collar 62 next to the hubis the stop flange 65, being secured thereto by welding or otherpreferred means. The stop flange is extended radially at one point onits periphery to form an ear 66 as shown. The purpose of thisconstruction is to permit of ready angular adjustment'of the ear 65 onthe stop flange 65 in relation to the distributor arm to enable propersetting of the rest position of the brushes 46 to be made.

To the top of the-hub 31 is demountably assembled the friction cup 61,held from rotating by a sliding pin and hole arrangement (not the boreof the hub to the friction washer iii to provide lubrication of theseparts. The friction nut is adjusted until the distributor arm is drivenwith little if any slip. The arrangement shown permits of an easilyadjustable, smooth acting friction drive for the distributor arm whichis found to stay in adjustment for extended periods.

The clutch mechanism Referring'to Figs. 13, 14, 15 which show-the Theupper portion of the friction cup assembly of mechanism by whichsynchronism is established, adjacent to the rolls 59 and 63 and withaxis parallel with the shaft 55 is rotatably mounted the double cam 12located so as to engage circurnferentially the rolls 59 and 63. The cam12 rotates on the spindle 13 mounted perpendicularly on plate 14 byriveting. Underneath the cam 12', slidably mounted on plate 14, is thecam detent 15. The cam detent 15 pivots at one end on the pivot pin 16.In the middle section of the cam detent is a curved slot 11, throughwhich extends the stud screw 18. This tween the slot 11 and the pin 18,is located a small hole 83, thru which is assembled the crank-shaped endof the operating link 94. The other end of link 84 is threaded and to itis assembled the adjustable clevis 85. The clevis is assembled to thearmature l8 of the release relay l5 by a pin 88.

The cam 12 is provided with a projecting upper stop 81, located on thetop surface, and diametri-s cally opposite the lower stop 82. This upperstop 81 is engageable by the the ear 55 of the stop flange 65 in oneposition of the cam 12. The diameter of the cam 12 is reduced at themiddle by the groove (see Fig. 16). Extending into and across the groove98 is the accelerating spring 9| which bears near its outer end againstthe accelerating pin 92, as shown. The accelerating spring 9| is loopedin several turns around a pin 93 rigidly mounted in the plate 14. Thefixed end 94 of the accelerating spring 9| bears against the pivot pin16. The accelerating pin is so formed that when assembled as shown, thefree end bears with moderate pressure against the accelerating pin 92.

The circumference of the double cam is serrated with a straight knurlexcept over an arc of approximately 90 in the region of the upper stop81, where the radius is reduced and the cam edges are left smooth. Thisare of the cam clears the rolls 59 and 88 when adjacent thereto.

The operation of the clutch mechanism is as follows: When the parts ofthe mechanism are in the position shown in Fig. 13, the short pawl 80engages the lower stop 82, stopping thedouble cam in such position thatthe upper stop 81 is virtually on the line of centers of the rolls 58'and 63 and the double cam 12. In this position the smooth edge of thecam is adjacent the rolls 59 and 63, providing clearance therebetween.The hub 31 can therefore continue rotation until the ear 66 engages theupper stop. 81, which stops the motion of the hub and the brush arm I3is stopped in the rest position on segment 8 as shown in Fig. 5. Sincethe hub 81 is frictionally driven, the drive shaft 55 and the roll 59continue in rotation.

Assuming now that the release relay I5 is energized, the armature 8pulls the link 84 which in turn draws the cam detent 15 away from thecam. The short pawl 88 is thus pulled out of engagement with the lowerstop 82, releasing the cam 12. The, detent 15 is drawn to the positionshown in Fig. 14. The accelerating spring 9| by exerting force on theaccelerating pin 82 causes the cam 12 to rotate quickly in acounterclockwise direction. This rotation of the cam 12 brings itsserrated edges into engagement simultaneously with rolls 59 and 88.Since roll 59 is secured to the drive collar 51, and roll 58 to the hubcollar'62, when the cam serrations grip the rubber rolls 59 and 68, thehub 81 is virtually locked to the drive shaft. It is to be noted thatthis is not a friction clutch, since the serrated cam edges mesh withthe rolls 59 and 88 without slipping and as tho geared thereto.

The cam 12 is rotated by reason of being engaged by roll 59, and theupper stop 81 is rotated away from the ear 88, removing these membersfrom engagement. The cam' 12 continues to rotate until it reaches theposition shown in Fig. 14, when the lower stop 82 comes into engagementwith the long pawl 8|, stopping the cm. In this position the smooth arcis adjacent the rolls 59 and 88 and the hub 81 is freely driven by thefriction drive previously described. The ear 88 passes clear of theupper stop 81 as shown in Fig. 14.

Should the release relay I5 become deenergized, the armature I8 ispushed back by spring l1, and link 84 pushes the detent 15 back into theposition shown in Fig. 13, disengaging pawl 8| and lower stop 82. Theaccelerating spring 9|, which has been placed in tension on theaccelerating pin 92 by the rotation of cam 12, now rotates cam 12 thru ashort are, bringing cam 12 in the position shown in Fig. 13. When theear 66 arrives at the upper stop 81, the hub is stopped and conditionsare restored as at the beginning of the cycle described above.

It is to be observed that the mechanism just described provides adefinite, but adjustable, stop or rest position for the brush arm i8;that on operation of the release relay l5 the driving shaft 55 and hub81 are quickly clutched together in a positive manner to bring the hub81 up to the speed of the drive shaft; that the positive action of agear clutch is obtained without the difllculty of possible clashing ofgears if engaged in the wrong position; and that the clutch action iscontrolled with the application of but little force on the part of theclutch release magnet. The accelerating spring 9| minimizes the intervalrequired for the clutch to act after the release relay is energized.

It is obviously possible to eliminate the clutch mechanism and cause thelink 88 to engage and stop the car 56 without the intervention ofadditional mechanism. The frictional torque of the friction drive is,however, restricted to a small amount, otherwise the pull of thecorrector magnet 36 will be insufhcient to overcome the frictionaltorque. The proper frictional torque for good correcting action isincapable of acceleratreliably come into position between the poles 58when the hub is accelerated solely by the normal frictional .drivingtorque. Theobiect of the clutch mechanism is therefore to establishsynchronism in a single revolution in a certain and reliable manner.

The release relay Referring to Figs. 13 and 17, which show the releaserelay l5 and associated parts of the circuit, comprising part of thepresent invention, the relay proper is of a well known type, commonlyreferred to as a telephone relay. On the core I! is assembled a lowresistance coil 28 of a comparatively few turns concentrated at thearmature end of the core. Next in order is a high resistance winding 2|of several thousand turns, occupying the central part of the corelength. At the heel end of the core is assembled a concentric sleeve orslug" of copper 28. The,

coils 28 and 2| are wound in the same direction and the adjacentterminals of the windings are wound slow releasing relay. when suppliedwith a pulse of suflicient magnitude and of considerable duration, suchrelays normally operate in from .004 to .006 second, and release in from.08 to .28 second after being fully energized. In high speed printingtelegraphs, however, the signal impulses are of very short duration, thecomplete pulse interval being of the order of .003 to .005 second. Arelay of the usual type designed to have a release time of .25 to .30second, i. e. the time required for the distributor arm to make onerevolution, plus a margin, will not respond to impulses of shortduration, for the reason that the copper slug required to produce suchdelay in release time is of comparatively large size, and prevents byits reaction the storing of the required amount of magnetic energy inthe magnetic structure of the relay. To overcome this difllculty, whichis inherent with this type of relay, a storing condenser 22 is connectedin shunt across the terminals of the high resistance winding 2|. Thiscondenser should normally be of considerable capacity, values of from 2to 16 microfarads, depending on the release time desired, having beenfound to give good results. With this condenser added to thecombination, the operation of the release relay I5 in response tocurrent impulses of short duration is as follows: When the synchronizingpulse is applied to the circuit shown in Fig. 17, a rush of currentflows thru the low resistance coil 20 into the storing condenser 22,which because of its large capacity offers comparatively littleimpedance to such rush of current, particularly at the beginning. Thisrush of current thru coil 20 magnetizes the core I0 at the armature endand attracts the armature I6. The reaction of the high resistance coil2| and the slug 23 are ineffective to prevent the coil 20 frommagnetizing the armature end of the core I5, because of their remotenessfrom this section of the core, and because of the high inductance of thecoil 2I.' Thev counter E. M. F.

generated by transformer action in coil 2| by the current in coil 20does not oppose the current in coil 20, but is utilizedto aid incharging co ndenser 22. The maximum energy is thus stored in the chargeof condenser 22. On the decay of the pulse current, this energy,combined with that stored in the coil 2| and the slug 23, operatetomaintaln the magnetic flux in the core, in accordance with Lenzs law.The armature is thus held firmly to the core during the decay of thepulse and thereafter. The release time is controlled by the amount ofcharge on the condenser 22 and the time required for the current thrucoil 2|, due to this charge, to decay until the holding current in thecoil 2| drops below minimum value. The variable resistor I9, located inthe circuit as shown in Fig. 17, provides a convenient means foradjusting electrically the release time of the relay without thenecessity of change in design, or mechanical adjustment of the relay. Itis to be noted that the location of resistor I9 in the circuit is suchas not to interfere with the operating pulse, but acts only to retardthe discharge of condenser 22 thru the coil 2|. Where such adjustment ofthe release time is not required, the resistor 22 may be omitted withoutdetriment, provided the resistance required to produce the release timedesired is incorporated in the coil 2|.

It is to be noted that the role of the slug 23 is materially diiferentin the present invention from that played in the types of slow releaserelays heretofore known. In such prior types,

the release time is mainly dependent on the energy induced in the slug(stored in the form of circulating current) by change in the magneticflux in the core I5. In the present invention, the release time iscontrolled almost exclusively by the charge on the condenser 22 and thecharacteristics of the coil 2|, any contribution from the slug beinginconsequential. For certain values of capacity of the condenser 22 andof inductance and resistance of the coil 2|, an oscillatory discharge ofenergy between the condenser 22 and coil 2| may occur. For othercombinations, a reversal of flux may occur when the circuit includingthe windings of the release relay is broken. In such instances the relaymay release the armature I6 momentarily, causing an unwanted drop out.The slug 23, by its damping action, opposes sudden magnetic changes, andcauses the relay to hold without chatter or release during transientconditions in the circuit. The damping action of the slug 23 is ofimportance in cases where the relay tends to chatter or drop outmomentarily. In cases where such tendencies do not exist, the slug 23may be dispensed with.

The relay described is capable of quick operation when supplied withimpulses of short duration; of holding firmly over periods of as much asa second after the energizing current has been cut oil; and of beingre-energized by short current pulses recurring periodically. It isfurther characterized by the principle of storing the energy for holdingthe relay in an operated condition in an associated condenser, whichcondenser is charged partly by the pulse current and partly by energygenerated in the holding winding by transformer action from the operat-The motor governor Referring to Figs. 18 to 21 inclusive, the motorgovernor I00, which is of the electrical type,

consists of a disc IOI of insulating material, mounted on a hub I02,which in turn is mounted on the motor shaft I03 by set screw I04. On theperiphery of the disc IOI are mounted two slip rings, I04 and I05, bywhich means current is led to the governor. The contact bracket IIII isheld in place by two screws IIO which pass thru the disc IOI andterminate in slipring I04 making electrical contact therewith. In theupturned portion of the bracket IN is threaded the adjustable contactscrew III having at the end a contact I I2.

The governor bracket I00 mounts the kinetic members, namely the tongueH3 and the governor spring II 4. The tongue H3 is of specialconstruction, consisting of a flexible strip H5, and a bi-metal stripIIG secured together by rivets III, as shown (see Fig. 20). As is wellknown, bi-metal consists of sheets of two metals of dissimilarco-eflicients of expansion, usually welded together to form onelaminated sheet or strip. It has the property of exhibiting curvaturewhen heated, the degree of such curvature being to a certain extentproportional to the change in temperature from the particulartemperature at which the bi-metal is flat or straight. Metals commonlyused in producing bi-metal are brass and steel, and brass and Monelmetal.

At the outer end of the bi-metal strip I I5 is mounted the movablecontact I I8, positioned to lie fiat against the stationary contact II2when governor bracket their surfaces are in contact. The tongue H3 isconveniently mounted on support 128 by means of a screw i221 and clampE22. lhe support E26 is part of the governor bracket I88. Near themiddle of the tongue is a hole into which is inserted the swivel pini133, having a hole into which is threaded one looped end of thegovernor spring H5. The governor bracket I08 is mounted on the disc idlby two screws H9 at one end, which screws terminate in the slip ringmaking electrical contact therewith. The contact bracket and thegovernor bracket WE are insulated electrically, except when the contactsH2 and iii are closed. A portion of the upturned to form the supporti225 upon which is mounted the flexible adjusting lever The free end ofthe adjusting lever is turned inwardly and is perforated by a small holeinto which is threaded a looped end of the spring EM as shown. Betweenthe bent portion of the'adjusting lever I and the support the adjustinglever is pierced by a hole, thru which is assembled the micrometeradjusting screw 52%, screwed into the support member i2l.

The operation of the governor is as follows: Assume that the governor isrotating in a counterclockwise direction as viewed in Fig. 18. At aparticular speed, the centrifugal force on the tongue M3 will exceed thespring tension in the 1 spring H4, and the contacts I I2-II8 will open.When these contacts open, the resistance R2 is inserted in series withthe motor as shown in Fig. 21. The motor is thereby slowed down, causingthe contacts to close, again speeding up the motor. This process isrepeated many times a second, the motor not reaching a stable speed, butvarying minutely above and below the speed at which the contacts open.This type of governor is well known, and it is to be observed that boththe inertia of and centrifugal force on the tongue H3 contribute to theregulating action. It has therefore been called a centrifugal-inertiagovernor. It is characterized by its sensitivity and accuracy ofregulation.

The novel features of the present invention reside in the means fortemperature compensation and for minor speed adjustment. It is evidentthat the tension in the spring Ill determines the speed to which themotor is regulated.

An increase in the temperature of spring Ill results in a slightdecrease in its tension, lowering slightly the regulated speed of themotor. This efiect is compensated for in two ways. The governor bracketI08 is held in position at one end by screws H9, the other end beingfree to move endwise only. The tensloning lever I25 and the adjustingscrew I26 are mounted at the free end of the governor bracket I 88. Asthe temperature of the governor increases, the governor bracket I08 isextended endwise by thermal expansion, stretching to a slight extent thespring H4, thereby increasing its tension and compensating in part forthe decrease in tension due to temperature. The compensation gained bythis means is limited, however, by the thermal expansion of the materialof the governor bracket along its length, and since the length of wirein the spring is much greater than the length of the governor bracket,compensation over a considerable range of temperature is not readilyaccomplished by this means alone. The second temperature compensationmeans is provided by the bi-metal strip H6 forming part of the tongueH3. As shown in Fig. 20, in exaggerated form,

when the temperature of the bi-metal strip II 8 is increased, it curvesconvexly outward. Due to this curvature, the tension of spring H4 is increased with increase of temperature, compensating for its normal lossof tension with increase of temperature. By using proper bi-metalcombinations and proportions of parts, determinable by well understoodmethods, thermal compensation of the governor may be accomplished over aconsiderable range of temperature.

With this improvement, the type of governor shown will regulate thespeed of the motor with a high degree of precision under variousconditions of temperature.

Minor speed adjustments It would appear that the resistance R2, commonlycalled the gap resistance, if sufiiciently large to slow the motor downto the speed set by the governor, would have little effect on the speedset by the governor. Such is the case, but a minor change in speed doesresult from a comparatively large change in the value of the resistanceR2. According to the present invention, this effect is utilized toaccomplish minor adjustment of the motor speed, without mechanicaladjustment of the governor, the value of R2 being variable for thatpurpose.

It is to be noted that changing the value of the gap resistance R2 isnot equivalent to introducing a similar resistance into other parts ofthe motor circuit. Resistance placed in series with the motor, forexample, has the same efiect as a change of load, and is counteracted bythe governor. The effect of such series resistance is also to impair therange of regulation of the governor. A relatively large change in thegap resistance R2 does not limit to any material extent the range ofregulation of the governor, but does produce a minor change in the speedset by the governor.

In printing telegraph systems, it is sometimes desirable to cause thesending instrument to run slower by a constant amount than does therecelvlng instrument, or vice versa. In the present invention a changein the gap resistance is utilized to effect the desired constant speeddiflerence. For this purpose, a resistance RI is placed in series withthe variable gap resistance R2 but is normally short circuited by thecontacts I88 I08. When these contacts are closed, the motor speed isregulated by the governor gap resistance R2 as previously described.When the contacts are open, additional resistance is introduced in thegap, and a minor but constant decrease in speed results. It is obviousthat the same arrangement, considering as normal the speed when contactsIflS-l 08' are open, will produce a minor increase in speed when thecontacts IDS-I08 are closed. The contacts III9.I08 may consist of aswitch, for local operation, or of the contacts of a relay 1 or remotecontrol.

It is thus clear that the present invention provides a novel method oftemperature compensation and minor speed control and adjustment for anelectrical governor. I The improved governor herein described is highlyaccurate, rapid and sensitive in action, self compensating fortemperature changes, adapted to minor speed adjustments without stoppingthe governor or changing its mechanical adjustments, and particularlyadapted to control of incremental speed changes by remote control.

Spring link feature As previously stated, the signal impulses and

